Publication date: 10th April 2024
I will share two recent studies on ceria:(1) The band structure of ceria influences not only its conductivity but also its reactivity. Yet operando experimental studies investigating the correlation between the 4f band and surface reactivity are still rare. To bridge this gap, we developed synchrotron-based operando ambient pressure X-ray photoelectron spectroscopy relaxation. This enabled us to study the surface redox kinetics of atomically flat CeO2 ultra-thin films under different biaxial strains (-3.27% to 3.55%), by monitoring the f band while altering pO2 more than 10 orders of magnitude within a minute. We discovered that tensile strain significantly enhances surface redox kinetics. Ab initio calculations suggest that tensile strain reduces the energy barrier of the surface redox reaction and promotes oxygen vacancy formation. Moreover, tensile strain decreases the band gap of ceria by lowering the conducting band's energy level, thereby facilitating easier charge transfer. (2) Recently study found the acidity of surface-infiltrated binary oxides can act as a descriptor for oxygen exchange kinetics in mixed conducting oxides such as Pr-doped ceria. We performed operando quantitatively modulation of alkaline oxide on Pr-doped ceria surface, using an integrated system of pulsed laser deposition, RHEED, impedance, and a glovebox. We observed a 'volcano shape' in oxygen exchange kinetics as the amount of alkaline oxide increased, with peak performance being ten times better than in ex-situ experiments. We propose that the interface of alkaline oxide/ mixed conducting oxide significantly aids the formation of oxygen vacancies, thus enhancing oxygen exchange kinetics. We believe that these two studies will spur further development of in situ kinetic studies of mixed ion-electron conducting oxide materials.
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